When key bolts are used, it is highly essential that the pins be securely locked against accidental or inadvertent removal or displacement, but also be readily removable when desired. Some prior pins fail to provide a positive, infallible locking means for releasably retaining the pin in such locked position, particularly with bolts of one-half inch diameter or less.
The present inventor has four prior patents relating to this field of art. In U.S. Pat. No. 3,476,007, issued 4 Nov. 1969, a key bolt is taught that has a bolt slot at one end of the shank portion of the bolt. A generally planar key fits into the bolt slot and a pin retains the key in the bolt slot by passing through a key slot in the key. In an unlocked position, the key extends directly outwardly from the shank and forms an extension thereof. The key slides and rotates within the bolt slot to a looked position where the key is substantially perpendicular to the shank. In the preferred form of that invention, the key has a portion of one of its side walls severed or partially severed so that the severed portion can have its free end offset from and protruding out of the plane of the key. The abutment of this severed portion against the bolt shank helps to retain the key in the looked position, and the severed portion can be moved to a position within the plane of the key sufficiently that the key is movable within the bolt slot.
U.S. Pat. No. 3,673,910, issued 4 Jul. 1972, is a continuation-in-part of the present inventor's '007 patent. In the preferred embodiment of this patent, the bolt slot of the '007 patent is replaced by a shelf-type recess wherein the key is slidably received atop the shelf-type recess. The key is held atop the recess by a pin. The key used in this variation has essentially the same type of bent offset severed portion of one of the side walls as is taught in the '007 patent.
U.S. Pat. No. 3,861,267, issued 21 Jan. 1975, is a division of the application which became the present inventor's '910 patent. The key taught in this patent has its locking feature provided by having one side wall have a portion of its outer edge formed into a downwardly turned flange that extends outside of the plane of the key, which is otherwise generally planar. To urge the key against the recess and into the locking position, a resilient means is positioned between the free end of the pin and the key.
U.S. Pat. No. 4,207,794, which issued 17 Jun. 1980, teaches a key bolt in which the key is slidably movable within a transverse aperture in the shank. Unlike the earlier three patents, this key does not rotate when moving from the locked to the unlocked position. Instead, the key has an unlocked position in which it is fully retracted inside the shank and a locked position in which it is extended perpendicularly outward from the shank. A resilient portion and a positive abutment means on the key prevent inadvertent retraction of the key into the aperture.
These key bolts are useful and effective, but practical experience of the inventor has taught him that practical limitations arise when the bolt shank goes below a certain minimum diameter. Typically this is observed at a diameter around one-half inch, although the key bolt of the type taught in the '794 patent becomes troublesome at even larger diameters, around one inch.